Seed fate of Marah macrocarpus (Cucurbitaceae) following fire: do seedlings recruit from rodent burrows?

Abstract

For numerous species in fire-prone ecosystems, the passage of fire triggers the release of large quantities of seeds within 2 years of the fire. This special case of masting has been described for species in an array of floras, but few studies have followed the fates of seeds liberated into the postfire environment. In this study, I followed the fates of 990, magnet-bearing Marah macrocarpus seeds sown at three seed densities in a large, high-intensity burn area. Seeds disappeared over 6.6 months and removal at all three densities became negatively density-dependent in late summer until all seeds disappeared in mid winter. I recovered only 5% of the magnets, mostly from rodent tunnels. Based on the recovery of magnets, I estimate rodents moved ~91% of the seeds belowground. Seed burial trials showed that seedlings established from seeds buried up to 16 cm whereas seeds sown on the surface did not germinate. Seedlings also readily established from burial in soils with 50% rock fragments as well as from artificial tunnels in both pot and field experiments. Excavation of 50 natural seedlings suggested up to 20% established in rodent burrows. Findings of this study suggest that ecologists may have underestimated the role of burrows as locations for recruitment of large-seeded species.